Fix OpenRouter BYOK prompt caching disabled — excessive token costs for Claude models in agent mode

What this error means

OpenRouter BYOK: Claude models do not benefit from prompt caching, causing excessive token costs in agent mode is a OpenRouter failure pattern reported for developers trying to resolve openrouter silently disabling prompt caching for anthropic claude models via byok, causing full-context resends at full price in long agent sessions. Based on the imported evidence, treat this as a tool-specific troubleshooting page rather than a generic API error.

Why this happens

microsoft/vscode#312939 — When using OpenRouter BYOK with Claude models in GitHub Copilot, prompt caching is silently disabled. Every agentic request re-sends full conversation context at full price. High billing impact for paid users. Category mapping: OpenRouter with API compatibility issue → OpenAI API (context-dependent mapping per SKILL.md).

Common causes

• microsoft/vscode#312939 — When using OpenRouter BYOK with Claude models in GitHub Copilot, prompt caching is silently disabled. Every agentic request re-sends full conversation context at full price. High billing impact for paid users. Category mapping: OpenRouter with API compatibility issue → OpenAI API (context-dependent mapping per SKILL.md).

Quick fixes

1. Confirm the exact error signature matches OpenRouter BYOK: Claude models do not benefit from prompt caching, causing excessive token costs in agent mode.
2. Check the OpenRouter account, local tool state, and provider configuration involved in the failing workflow.
3. Compare the failing environment with a known working setup, then change one configuration value at a time.

Platform/tool-specific checks

• Verify the command, editor, extension, or API client that produced the error.
• Compare local settings with CI, deployment, or editor-level settings when the error appears in only one environment.
• Avoid deleting credentials, local model data, or project settings until the failing scope is clear.

Step-by-step troubleshooting

1. Capture the exact error message and the command, editor action, or request that triggered it.
2. Check whether the failure is account/auth, quota/rate, model/provider, local runtime, or deployment configuration.
3. Review the source evidence below and compare it with your environment.
4. Apply one change at a time and rerun the smallest failing action.
5. Keep the working fix documented for the team or deployment environment.

How to prevent it

• Keep provider/tool configuration documented.
• Record non-secret diagnostics such as tool version, provider name, model name, and command path.
• Add a lightweight check before CI or production workflows depend on the tool.

Sources checked

• https://github.com/microsoft/vscode/issues/312939

Evidence note: microsoft/vscode#312939 — When using OpenRouter BYOK with Claude models in GitHub Copilot, prompt caching is silently disabled. Every agentic request re-sends full conversation context at full price. High billing impact for paid users. Category mapping: OpenRouter with API compatibility issue → OpenAI API (context-dependent mapping per SKILL.md).

Related errors

• OpenAI API

FAQ

What should I check first?

Start with the exact OpenRouter BYOK: Claude models do not benefit from prompt caching, causing excessive token costs in agent mode text and the smallest action that reproduces it.

Can I ignore this error?

No. Treat it as a failed OpenRouter workflow until the root cause is understood.

Is this guaranteed to have one fix?

No. The imported evidence supports the troubleshooting path above, but tool behavior can vary by account, plan, version, provider, and local configuration.

How do I know the fix worked?

Rerun the same command, editor action, or request. The fix is working when that action completes without OpenRouter BYOK: Claude models do not benefit from prompt caching, causing excessive token costs in agent mode.